Westmoreland, NH (PRWEB) May 31, 2012
Thermally and chemically sensitive areas of PCBs (contacts, components, etc.) need to be protected (masked) during the harsh wave flow, reflow, wash, conformal coating, etc. processes they are subjected to during their manufacture. In addition, with the dramatic increase in PCB power and functionality, more and more PCBs are also sensitive to electrostatic charges. These charges can arise from the masking process and, if not properly dissipated, can produce electrostatic discharge (ESD) that can potentially damage the PCB and result in increased warranty and liability.
ESD can potentially damage PCBs during manufacturing, assembly and test. ESD occurs when electrostatic charges are allowed to build up on a surface to the point where they discharge to ground. Depending on the severity of the discharge, static sensitive components and devices on the PCB may be damaged which drives up manufacturing costs. In addition, if the damaged PCB is not detected, it can make its way to assembly and eventually into the hands of consumers greatly increasing warranty cost and liability risks.
The electrostatic charges that create the potential for ESD are generated when dissimilar materials come in contact with PCBs primarily via tribocharging (physical contact). The charges can come from applying masking tape to the board (to protect thermally and chemically sensitive areas of the board from wave flow, reflow, wash, etc processes), from human contact or contact with manufacturing equipment, fixtures, slides, clamps, conveyors, slides, robots, etc.
The ESD Association estimates that product losses due to ESD in microprocessor-based electronics manufacturing account for 6.5% of annual revenues. In addition, if these discharges are not prevented during the initial PCB manufacturing, the cost of failure (warranty, liability, safety, etc.) increases by a factor of 10 for each step until final consumer use.
Aerospace OEM Turns to Polyonics
A large West Coast electronics OEM determined that the tape used to protect their PCBs during wave flow was adding electrostatic charges to the boards. In addition, a conveyor used to transport the boards between processes was adding additional charges. Both situations were causing damage to their boards through ESD events. The OEM needed a single tape that would protect sensitive areas of PCBs from all three threats...heat, chemicals and static charges.
The OEM turned to the Polyonics family of high temperature antistatic tapes. The tapes helped protect their PCBs from the wave flow heat and chemicals along with ESD. This allowed them to increase product performance and component and board reliability while decreasing manufacturing and warranty costs.
The tapes they used included XT-622 (1mil PI), XT-623 (2mil PI) and XT-627 (2mil PET) and are rated up to 500C for the polyimide and 400C for the PET models. The tapes provided the OEM with low peel voltage (see peel voltage chart upper right) when their liners were removed during masking plus, having surface resistances of 10^5 to 10^9 Ohms (see surface resistance chart bottom right) they also dissipated any charges that occurred during subsequent manufacturing processes.
Polyonics uses TriboGard technology to create both antistatic and static dissipative performances in their tapes. The charge density chart (second from top right), illustrates that when electrostatic charges are deposited on insulative surfaces they tend to stay indefinitely and charges deposited on conductive surfaces discharge quickly, potentially damaging static sensitive components (SSD). However, when charges are deposited on dissipative surfaces, such as Polyonics high temperature antistatic tapes, they are safely discharged protecting the surfaces from possibly harmful ESD events
TriboGard™ technology produces a static dissipative top layer on the tape with a surface resistance of 10^5 to 10^9 Ohms. In addition, the technology provide low peel voltage (<100v) when the liner is removed. For temporary applications such as PCB masking, where the antistatic tapes are used during a portion of the manufacturing process, the tape will again, depending on the severity of the process, produce a low peel voltage (<100v) when removed from the substrate helping to further prevent an ESD event from occurring. This combined 360° ESD protection helps prevent the buildup of electrostatic charges during manufacturing and assembly and protects the PCB from possibly spikes in current during operation that could damage the component or device. In addition, depending on the severity of the process, the tapes will also leave insignificant residue once removed.
Polyonics antistatic tapes are offered in both single and double-coated versions. They can be constructed of amber or black polyimide, polyester (PET) and aluminum. The double-coated antistatic tapes provide a unique bonding system that also helps protect static sensitive devices (SSD) from ESD events. Both single and double-coated tapes are designed to be die cut and auto-applied with the double-coated versions providing additional stiffness, compared to traditional transfer tapes that.